Conventionally, there are two developing methods which employ dry developers a method using a developer of two-component system and a method using a developer of one-component system.
The method using the developer of two-component system uses a developer of mixture of toner and carrier, and therefore a toner density controlling apparatus for keeping the mixing ratio of toner and carrier constant is necessary. This method also has the deficiency that the developer must be of periodically replaced because of deterioration of the carrier and the like. For this reason, in recent years, to eliminate the above-mentioned deficiencies, a developing method by only a developer of one-component system which uses no carrier has been proposed.
This method is shown, for example, in the Japanese Published and Unexamined Patent Application No. sho 54-43038 and the U.S. Pat. No. 4,083,326, and the configurations thereof are shown in FIG. 1 and FIG. 2.
In FIG. 1 (Japanese Published Unexamined Patent Application No. sho 54-43038) numeral 1 designates a developing roller consisting of a cylindrical sleeve incorporating a magnet, numeral 2 designates a magnetic toner, numeral 3 designates a hopper, numeral 4 designates a blade and numeral 5 designates a photoreceptor. The developing roller 1 is constituted with a metallic material having an uneven surface, and the toner 2 is supplied from the hopper 3. Next, when the developing roller 1 is rotated in the direction as shown by an arrow, the toner 2 is charged in a predetermined polarity by the blade 4 brought in slide-contact with the surface of the developing roller 1, and is coated on the surface of the developing roller 1. Next, the charged toner 2 flies to develop when facing an electrostatic latent image of the photoreceptor 5.
In FIG. 2 U.S. Pat. No. 4,083,326), numeral 13 designates a developing roller, numeral 14 designates a toner, numeral 15 designates a hopper, numeral 16 designates a blade, numeral 17 designates a sheet-shaped photoreceptor, numerals 18 and 19 designate conductive fur brushes brought in slide-contact with the developing roller 13, numeral 11 designates a first power supply applying a voltage to the hopper 15 and the conductive fur brush 18, and numeral 12 designates a second power supply applying a voltage to the conductive fur brush 18 and a developing roller 7. Also, constitution is made in a manner that the voltage applied by the second power supply 12 is larger than the voltage applied by the first power supply 11, and is lower than the voltage of the electrostatic latent image of the photoreceptor 17. The toner 14 friction-charged by the fur brush 18 is supplied from the hopper 15 to the developing roller 13 through the conductive fur brush 18 by the potential difference between the first power supply 11 and the second power supply 12, and is subsequently smoothed by the blade 16, and adheres to the electrostatic image of the photoreceptor 17 to develop. Subsequently, after development the toner 14 on the developing roller 13 is scrubbed off by the conductive fur brush 19 to remove the hysteresis of development on the developing roller 13.
However, the method employing such a system has problems in forming a uniform thickness of layer of the developer (toner) on the developing roller and in charging characteristics, which make it difficult to reproduce a high-quality image. This means that, in FIG. 1 and FIG. 2, the toner adhering onto the developing roller 1 or 13 in a layer by rotation of the developing roller 1 or 13 is brought in contact with the blade 4 or 16, and is formed into a thin layer while scrubbed off in sequence from the uppermost layer. At this time, depending upon the position of the blade 4 or 16 pressed onto the developing roller 1 or 13, agglomerated toner is produced on the developing roller 1 or 13, or stripes are produced in the rotating direction or the axial direction of the developing roller 1 or 13, and thereby the layer thickness and the amount of charge of the toner on the developing roller 1 or 13 are varied, and resultantly an uneven density and toner scattering take place in developing, making it difficult to reproduce a high-quality image.